This button will do what you want, after you change the Layout name to the one you use by default.
<?xml version="1.0"?>
<button display="both">
<label>Save All Listers as Default Layout</label>
<tip>Save all open Listers as the default Lister Layout (change name accordingly)</tip>
<icon1>199</icon1>
<function type="normal">
<instruction>Prefs LAYOUTSAVE LAYOUTNAME="Default"</instruction>
</function>
</button>
Read This FAQ: How to add example buttons to your toolbars and menus